This invention relates generally to wire clamp assemblies for electrical terminals and more particularly to a screw and washer wire clamp assembly for holding one or more wires in an engagement with a generally flat surface of a terminal block or the like.
Screw and washer type clamp assemblies including a screw for threadably engaging an internally threaded terminal member and a clamping washer advanced by the screw to clamp a wire to the terminal member surface are known in the art. For example, attention is directed to U.S. Pat. Nos. 3,177,456 and 3,816,820 and 4,146,289 which disclose clamp assemblies of this general type.
Many of the clamping washer members heretofore devised, however, do not sufficiently positively engage the wire to prohibit lateral or axial movement or twisting thereof after clamping, which may lead to mechanical or electrical failure of the connection. As a practical matter, resistance to extruding action in the wire during "pull-out" tests such as the UL 486 test must meet certain standards to gain approval of the terminal clamp device. Devices which fail to pass such tests are usually unsaleable.
Moreover, many clamping members are designed for connecting wires only in a limited range of sizes and are virtually inoperable when two wires of different sizes are to be connected to the same terminal. Various clamping washers heretofore designed for use in assemblies meeting the foregoing requirements have been relatively complex and correspondingly difficult and expensive to manufacture.
Additionally, it is important to make some provision in the terminal assembly and preferably in the clamping device itself for holding the clamped wire or wires out of excessive engagement with the screw portion of the assembly. In this regard, excessive contact with the screw threads during assembly and disassembly of wires with a terminal may cause damage to the wires, ultimately leading to mechanical or electrical failure of the installation. One particularly advantageous device which solves many of the foregoing problems is shown in U.S. Pat. No. 4,146,289. While this device has proven advantageous in use and has gained wide market acceptance, there remains room for further improvement.
In particular, it has been found that the pull-out resistance of such a clamping device may be surprisingly increased by the expedient of providing for a multi-location, tapered contact of the clamping washer with the wire to be clamped. Such multi-location engagement not only enhances the pull-out resistance of the wire but also enhances the resistance to forces tending to swivel the wire generally about the axis of the screw member of the assembly.